This invention relates to a two-way radio communication system of the simplex or half-duplex type having a communication link to a duplex telephone system. More particularly, the invention relates to such a radio telephone system wherein the simplex or half-duplex remote radio is provided priority to talk upon demand.
In simplex or half-duplex radio systems, the parties must take turns talking. In the duplex telephone system the called and calling parties may both talk and listen simultaneously. In a radio telephone interconnect call the requirement of taking turns to talk presents a problem of establishing the direction of the simplex audio path.
Voice responsive circuitry (VOX) has been employed to control the direction of the simplex audio path in such a radio telephone interconnect call. A simplex transceiver interfacing the simplex radio system with the duplex telephone system typically includes VOX circuitry that controls the simplex audio path direction. When the land party is talking the VOX circuitry enables the transmission to the mobile radio. When the land party stops talking, beep tones can be automatically generated by the VOX circuitry as an alert signal to the operator of the mobile radio that he can now talk.
When the operator on the mobile radio ends his message he can send a beep signal by manual control to similarly alert the telephone party and also to cause the transmitter at the interface transceiver of the radio system to be turned on, readying it for the next message from the telephone party.
VOX circuitry typically includes time delay circuits for maintaining the direction of the audio path during pauses in the land party's message. However, these delay circuits undesirably extend the transmit mode at the completion of the voice message from the land party.
Another major problem with VOX circuitry is the inability to satisfactorily give the mobile radio party priority to talk on demand. One technique, commonly known as periodic sampling, that is used with VOX circuitry for providing the mobile radio party such priority operates as follows. While the land party is transmitting, the received audio is periodically sampled at the simplex transceiver to determine if the mobile radio operator is attempting to talk. When the received audio is being sampled, the transmitter is disabled in the simplex transceiver. Thus, this periodic sampling results in the chopping of the audio tranmission by the land party, thereby producing unsatisfactory audio quality.
There exists a need for a two-way radio communication system of the simplex or half-duplex type having a communication link to a duplex telephone system wherein the simplex mobile radio is provided with priority to talk upon demand. Additionally, it is highly desirable to provide a communication method to eliminate delays inherent in VOX circuitry, and likewise to avoid the periodic sampling technique as employed with VOX circuitry in order to provide the mobile radio party priority to talk on demand.